Northern Mali, which fell under the control of al-Qaeda-linked groups in 2012 before a French-led military intervention pushed them out, remains vulnerable to attacks by fighters.

"At least two people were killed during an exchange of gunfire" as the hostage was being taken, a security source who wishes not to be named told AFP news agency, without revealing the identity of the victims.

"All roads to Mali are being monitored."

It is the first time that a US national has been kidnapped in Niger.

A US Department of State spokesperson told AFP that they were aware of reports of the kidnapping of an American citizen but declined to comment further.

Previous incidents

In January 2011, two young French people were kidnapped from a restaurant in Niamey and were killed shortly afterwards during a rescue attempt.

The previous year, five employees of the French energy firm Areva were kidnapped by al-Qaeda in the Islamic Magreb from a uranium mine in Arlit, north of the country.

Four men were freed in 2013 after the earlier release of the sole female hostage.

Earlier this month, 22 soldiers from Niger were killed during an attack by armed men who came from Mali to target a refugee camp in the Tahoua region, northeast of Niamey.